Excavator Electrical vs Hydraulic Diagnostic Flow Chart

(Start Here Before Replacing Anything Expensive)

START: MACHINE UNDERPERFORMING / ERRATIC / FAULTING

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STEP 1: DEFINE THE SYMPTOM TYPE

Is the problem:

• ❏ Constant (always present)

• ❏ Intermittent (comes and goes)

• ❏ Heat-related (worse when hot)

• ❏ Load-related (only under stress)

👉 Intermittent or heat-related symptoms strongly suggest ELECTRICAL👉 Constant, progressive symptoms suggest HYDRAULIC

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STEP 2: CHECK FOR ACTIVE FAULT CODES (DO NOT TRUST THEM YET)

Are fault codes present?

• ❏ Yes

• ❏ No

👉 Fault codes = reaction indicators, not root cause👉 Proceed regardless of code presence

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STEP 3: VERIFY ELECTRICAL FOUNDATION (NON-NEGOTIABLE)

Before touching hydraulics:

✔ Battery voltage under load

✔ Alternator output

✔ Main grounds (engine, frame, ECU)

✔ Key sensor reference voltage (usually 5V)

Any voltage drop, corrosion, or instability?

• ❏ Yes → FIX ELECTRICAL FIRST – STOP HERE

• ❏ No → Proceed

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STEP 4: IS THE MACHINE BEING COMMANDED TO WORK?

Check commanded vs actual values:

• Pump command

• Engine load request

• Solenoid duty cycle

• Travel / swing command

Is command LIMITED or DERATED?

• ❏ Yes → Electrical control or sensor issue

• ❏ No → Hydraulics allowed to perform → Proceed

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STEP 5: VERIFY MECHANICAL REALITY VS SENSOR DATA

Compare:

• Mechanical pressure gauge vs pressure sensor reading

• Actual RPM vs ECU RPM reading

Do sensor readings match reality?

• ❏ No → SENSOR / WIRING FAULT

• ❏ Yes → Proceed

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STEP 6: BASIC HYDRAULIC HEALTH CHECK

Measure:

✔ Main system pressure

✔ Pilot pressure

✔ Load sense pressure

Is pressure:

• ❏ Low everywhere → Suspect pump or system leakage

• ❏ Normal but weak function → Suspect valve leakage or electrical control

• ❏ Unstable → Valve wear or control issue

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STEP 7: CASE DRAIN TEST (TRUTH FILTER)

Perform case drain test on:

• Pumps

• Travel motors

• Swing motor (if applicable)

Case drain results:

• ❏ High → Hydraulic wear confirmed

• ❏ Normal → STOP BLAMING THE PUMP

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STEP 8: FUNCTION ISOLATION TEST

Disable or isolate:

• Individual solenoids

• Valve sections

• Pilot signals

Does isolating a circuit restore performance?

• ❏ Yes → Valve internal leakage or control issue

• ❏ No → Proceed

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STEP 9: SOLENOID & CONTROL VERIFICATION

Test:

✔ Solenoid resistance (cold & hot)

✔ Voltage under load

✔ Command stability

Is resistance or voltage unstable?

• ❏ Yes → Electrical fault

• ❏ No → Solenoid innocent → Proceed

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STEP 10: CAN BUS & COMMUNICATION CHECK (MODERN MACHINES)

Look for:

• Multiple unrelated fault codes

• Communication timeouts

• Modules dropping offline

CAN issues present?

• ❏ Yes → Network / wiring fault

• ❏ No → Proceed

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STEP 11: VALVE BANK VERDICT

At this point:

• Electrical verified

• Commands verified

• Pressures verified

• Case drain verified

Remaining symptoms now point to:

• ❏ Internal valve leakage

• ❏ Spool wear

• ❏ Cracked housing

• ❏ Pilot control instability

➡️ Valve bank inspection or test bench required

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FINAL DECISION POINT

Replace components ONLY when:

✔ Electrical supply is clean

✔ Signals match reality

✔ Hydraulics measured bad—not “felt” bad

THE GOLDEN RULE (PRINT THIS)

If hydraulics are weak, prove they’re allowed to be strong.If electronics look wrong, prove the hydraulics are stable.

WHY THIS FLOW CHART WORKS

✔ Prevents unnecessary pump replacement

✔ Stops valve banks being blamed for sensor lies

✔ Protects new components from repeat failure

✔ Separates cause from reaction

✔ Works across Volvo, Komatsu, Hyundai, Doosan, CAT